A commercially successful acoustical tile is marketed under the trademark ACOUSTONE and is made generally using the composition and procedures disclosed in U.S. Pat. No. 1,769,519. According to the teachings of this patent, a molding composition comprising granulated mineral wool fibers, fillers, colorants and a binder, in particular a starch gel, is prepared for molding or casting the body of the tile. This mixture or composition is placed upon suitable trays which have been covered with paper or a metallic foil and then the composition is screeded to a desired thickness with a screed bar or roller. A decorative surface, such as elongated fissures, may be provided by the screed bar or roller. The trays filled with the mineral wool pulp or composition are then placed in an oven for twelve (12) hours or more to dry or cure the composition. The dried sheets are removed from the trays and may be treated on one or both faces to provide smooth surfaces, to obtain the desired thickness and to prevent warping. The sheets are then cut into tiles of a desired size.
The mineral wool acoustical tiles of the prior art, as disclosed in U.S. Pat. Nos. 3,246,063 and 3,307,651, generally used a starch gel as a binder for the mineral wool fibers. The gel may comprise a thick boiling starch composition combined with calcined gypsum (calcium sulfate hemihydrate) which are added to water and cooked at 180.degree. F.-195.degree. F. for several minutes to form the starch gel. Thereafter, the granulated mineral wool is mixed into the starch gel to form the aqueous composition which is used to fill the trays.
Mineral wool acoustical tiles are very porous which is necessary to provide good sound absorption. The prior art (U.S. Pat. Nos. 3,498,404; 5,013,405 and 5,047,120) also discloses that mineral fillers, such as expanded perlite, may be incorporated into the composition to improve sound absorbing properties and provide light weight.
It is an object of this invention to provide an acoustical tile composition which contains no mineral wool.
It is another object of this invention to provide a mineral wool-free acoustical tile composition having acoustical properties comparable to the commercially available cast mineral wool tiles.
It is a further object of this invention to provide an acoustical tile composition comprising a combination of expanded perlite, a starch gel binder, reinforcing fibers, and an inorganic filler.
These and other objects will be apparent to persons skilled in the art in view of the description which follows.